The present invention relates to a cylinder liner having an inner peripheral surface provided with a surface treatment layer by a water vapor treatment, etc, and a method for processing the cylinder liner for use in an internal combustion engine.
In a cylinder liner for a conventional Diesel engine, phosphate treatment or nitriding treatment is performed to form a surface treatment layer on an inner peripheral surface of the liner in order to improve wear resistance. Then a honing is performed on the surface treatment layer on the inner peripheral surface of the cylinder liner for final machining to the inner surface. In the conventional final grinding to the inner peripheral surface, a resinoid bonded grindstone containing silicon carbide is used. The grain size of the silicon carbide is not more than 3000, and the silicon carbide is contained in an amount less than 50% in the resultant grindstone. As a result, the surface treatment layer has a cross-hatching pattern providing oil pockets which are advantageous for a lubricating property.
Recently, the diesel engine is subjected to a severe working condition due to a severe requirements in exhaust gas. Therefore, corrosion resistance as well as wear resistance are required in the cylinder liner. In order to meet with the demand, a cylinder liner having a surface treatment layer provided by a water vapor treatment is described in WO 01/33065A1.
The water vapor treatment forms a surface treated layer mainly formed of triiron tetroxide (Fe3O4) which provides sufficient wear resistance and corrosion resistance. However, because triiron tetroxide is extremely brittle and has high hardness, finishing or final machining to the inner peripheral surface of the cylinder liner subjected to water vapor treatment is extremely difficult in comparison with the machining to the inner peripheral surface of a cylinder liner formed with the conventional phosphate layer or the conventional nitriding treatment layer. Further, the difficulty in machining is increased in proportion to the increase in thickness of the water vapor treatment layer.
If the inner peripheral surface of the cylinder liner subjected to the water vapor treatment is machined by a honing machine using a conventional grinding wheel, excessive wearing of the grinding wheel occurs, and such honing requires a prolonged time period. If hardness of the silicon carbide is increased and grain size thereof is reduced in an attempt to provide a cross-hatching pattern on the inner peripheral surface of the cylinder liner, the inner surface is injured due to thrusting of the cutting chips into the inner surface.
Further, in the conventional technique, no attention is drawn to an initial break-in property of the cylinder liner, but attention is only drawn to an oil retaining property on the inner peripheral surface of the cylinder liner.